The present invention relates to a method of performing concentration determinations of aqueous solutions or of determining on-line the dosing concentration of polyaspartic acids and/or their salts in aqueous systems.
When treating water, it is very important to maintain a constant level of the chemicals used. Too low a dose of a scale inhibitor might, in a cooling water circuit, entail reduced heat transfer due to calcium salt deposits. If fresh water is fed in, this requires the treatment chemicals to be restored to their old levels and consequently requires a concentration determination.
Analysis of the scale inhibitor is performed photometrically or titrimetrically, depending on the substance. A more economical approach would be provided by a physical method in which a test parameter that depends linearly on the concentration of, e.g., the scale inhibitor is measured on-line and is kept at a constant value using a dosing apparatus or facility.
EP-A 485,882 describes the use, as a scale inhibitor, of a polymer labelled with a fluorescence label such as, e.g., coumarin or its derivatives, the concentration, having been correlated to the fluorescent intensity, being corrected to an optimal value either automatically or manually.
EP-A 475,602 describes a method of fluorescence labelling of polyacrylic acid esters or amides by reamidation using fluorescent amines such as, e.g., tryptophan. In the latter case, incorporation amounts to 76%, 15 mol% of tryptophan having been used. Detection was possible down to 1 ppm.
The patent U.S. Pat. No. 4,813,973 describes the preparation of fluorescence-labelled polymers for uses in the field of flocculants, papermaking,and petroleum drilling. This involves the reaction of amide-containing polymers such as polyacrylamide with water-soluble dyes such as 9-xanthydrol in acetic acid.
Thermal polyaspartic acid from maleic anhydride and ammonia is most recently increasingly being used as a biodegradable alternative to polyacrylates in many applications. In some cases, a rapid and specific concentration determination method is called for, such as that known for fluorescence-labelled polyacrylic acids.
It is an object of the present invention to develop a method applicable also to polyaspartic acids (“PASP”) for the purpose of determining concentrations in aqueous systems that allows permanent monitoring of the concentration of PASP in aqueous systems, in order thus to prevent, while plants are on-line, undesirable deposits in the form of inorganic or organic scaling from occurring while at the same time preventing the body of water from being polluted by excessive introduction of PASP as a scale inhibitor. The monitoring of the scale inhibitor should, moreover, function in flowing water streams and be feasible by on-line measurements.
Fluorometry is a widely used analytical measuring method in which a substance is excited by means of a light source (xenon lamp) and the intensity of the emitted fluorescent light is measured as a function of the excitation and emission wavelengths. It is used, inter alia, as a rapid, cost-effective “in situ” analysis method. Fluorescent spectroscopy is a recognized measurement method for measuring discharges into bodies of water. This involves the substances (i.e., active ingredients in a formulation) to be detected by being either chemically labelled by means of a label or being identified as a mixture using an added fluorescence label. Correlating the fluorescence label to the active ingredient proper is not always entirely simple. Problems arise from the differential breakdown behaviour on the thermal and the microbiological front. Moreover, masking, e.g., by complex formation, giving rise to passive fraction of the active ingredient, does not reflect a direct relationship to the label.
Consequently,such systems must always be employed in higher concentrations than strictly necessary. After all, too low a dosage of a scale inhibitor might, in a cooling water circuit, entail reduced heat transfer due to calcium deposits on the transfer surfaces.
Thermal polyaspartic acids from maleic anhydride and ammonia most recently are increasingly being used as a biodegradable alternative for polyacrylates in many applications. In water treatment in particular, thermal polyaspartic acid is intended to play a significant part in metal complexing and as a dispersant. One of the positive physical characteristics of thermal polyaspartic acids is their fluorescence. This should allow the active ingredient proper to be detected without any indirect measures. If this is to be done, linear dependencies of the fluorescent intensity on the concentration, breakdown (chemical, physical, or biological) or involvement as a dispersant or complexing agent would be desirable.